I had to grow filesystem on a production database by adding more disk to raid 10 but not thru concatenation as it would hit a performance but rather by recreating raid so proper config would be preserved. The trick is how to do it without any downtime. With VxVM you can do all of this on-the-fly without stopping database, unmounting filesystems, etc. and all of this on rather old Solaris 8 in a cluster environment (Sun Cluster). It took some time for VxVM to relayout data but at the end it worked without any problems or downtime of the database.
On the other hand it makes less sense to use VxVM (due to costs) as more features are put in SVM which is free with Solaris and as more features are put in mid-range and low-end arrays so a volume manager is not needed at all or SVM is good enough.
It doesn't mean of course that VxVM doesn't make sense in all cases - in many it does and it's really good software.